Early microcomputers employed buses which were direct extensions of the signal lines appearing at the pins of a microprocessor. As the technology associated with the latter components rapidly progressed, users and manufacturers recognized the value of some bus standardization to facilitate system upgrading or new electronic system designs. The advantage of compatibility at the local bus level was realized early and the electronics industry evolved a number of bus standards based upon the back-plane/bus specifications of more popular microprocessors and microcomputers.
Over a period of time, a number of official IEEE Bus Standards have been developed and are generally in varying stages of formal adoption. In addition, manufacturers and military and scientific users continue to define their own bus standards. Predominant among these standards is the "VME BUS", the term "VME" representing a back-plane/bus structure referred to as "versa module Europe", developed by Motorola/Mostek/Signetics-Phillips. A "VXI Consortium" of industry and government, the term representing an acronym for "VME BUS extension for instrumentation" evolved "VXI" specifications for a VXI/VME back-plane/bus.
In general, the back-plane/bus specifications look to the aspects of system environmental requirements such as air flow, power source derived voltage outputs, connector pin assignment, protocols and the like. Specified power supplies are required with the standards which are manifested as a sequence of voltage outputs which must remain within defined tolerances.
To complement the evolving sophistication of the back-plane/bus devices and systems, improvements in supporting power supplies also have occurred. In this regard, power-switching converters are becoming an essential part of many electronic systems as industry continues its quest for miniaturization. In general, the switching converter is a power electronic system that converts one level of electrical energy to another level, at the load, by switching action. These devices continue to exhibit higher switching frequencies, newer topologies, and new integrated-circuit controllers with attendant increased conversion efficiency and power-packaging density. In the latter regard, manufacturers of these power supplies offer them as "bricks", the small devices generally being rectangularly shaped packages of typically flat configuration, one side of which incorporates a heat transfer surface generally formed of aluminum. Because of their small size and interconnectability, the bricks are sometimes referred to as "modular power converters". These modular power converters typically are of a d.c.-to-d.c. variety, converting a higher level d.c. input voltage of about 180 to 400 volts to backplane/bus specified voltage values, for example for VME systems, of 5vdc, +12vdc, -12vdc, and -3.3vdc, or different combinations of such input levels. In utilizing these converter modules, power supply manufacturers combine them within a sub-housing which will include an air circulation fan or fans and supporting circuitry. The bolt-on outputs of the collection of converter modules within the sub-housing will be exposed at one of their ends for connection by cabling to corresponding power supply inputs at the backplane and elsewhere. This sub-housing containing the converter modules generally will be incorporated within a main housing holding the backplane and those functional circuit boards or "cards" connected to it along with chassis temperature controlling fans and the like. The use of such cabling has been problematic. These cables are typically of large gauge wire, for example from 12 gauge to as low as 0 gauge, having ring tongue lugs on them which are bolted to connectors using specified torques. Such cables may vibrate with time and loosen-up such that their current handling capability often is dependent upon how reliable the torqued connection remains. The inherent induction exhibited by cables imposes electrical delay which, without correction, is manifested in current delivery difficulties where the load requires a sudden pulse of relatively large current quantity, for example as memory banks are accessed. It is desirable to be able to draw such current from a low impedance or a capacitive source. Unfortunately, cables appear as a high impedance inductive source such that there would exist an undershoot of current supplied at the commencement of such current demand and a corresponding tendency for the current to be maintained or exhibit overshoot phenomenon at the termination of a demand pulse. This undershoot and overshoot characteristic occurs generally in immunity from the lengths of cable involved. While correcting circuitry is provided to accommodate this load-related phenomenon, its addition to a system, in itself, detracts from system reliability.
Over the recent past, chassis designs themselves have been the subject of significant improvement. Their general structuring of basically a "card cage", backplane, fans, and rearwardly mounted power supply sub-assembly originally was made available to users in that basic or simplistic format or structuring. Tracewell, in U.S. Pat. No. 5,168,171, issued in 1992, describes a mainframe enclosure which incorporated a microprocessor-driven support system functioning to monitor the status of power supplies, which provided an improved cooling air flow path and further provided temperature monitoring. Importantly, the status information and system controls were established at a user accessible supervisory panel mounted at the front face of the enclosure. Sold under the trade designation "Intelligent Mainframe", the improved enclosure design found ready acceptance in the electronics industry.
As electronic systems supported by mainframe enclosures continue to evolve in both sophistication and miniaturization, there is arising a concomitant call for more compact system size and, thus, more compact enclosures and system support components. These more compact systems preferably will include more efficient power delivery features exhibiting higher levels of operational reliability as well as compactness.